KR20030062252A - High heat transfer tubular reactor - Google Patents

Abstract

The gas phase tubular reactor in the shell heat exchanger basically comprises a porous wicking surface applied on the outer side of the reactor tube to remove the heat of reaction in an isothermal state. The porous wicking surface on the reactor tube withdraws the liquid heat transfer liquid from the reservoir at the bottom of the wicked tube portion to provide enhanced evaporative cooling. The present invention is particularly useful when the reaction selectivity is adversely affected by a heat generating reaction or a high temperature excursion.

Description

High heat transfer tubular reactors {HIGH HEAT TRANSFER TUBULAR REACTOR}

The present invention basically relates to a tubular reactor integrally formed with a heat exchanger, suitable for removing large amounts of heat from the reactor in an isothermal state.

Commercially important chemical reactions, particularly catalytic gas phase partial oxidation reactions, are carried out in tubular reactors, in which it is important to maintain the temperature of the reactants within a narrow temperature range in order to obtain the required production rates, selectivities and properties. Many of these reactions are fast and generate a lot of heat. These reactions are typically run at high temperatures in heterogeneous catalytic tubular reactors. Most of these reactors are formed as shells and tubular heat exchangers, where the tubes of the reactor are filled with the appropriate catalyst supported on a porous medium. The gaseous reactant is fed to the reactor tube and reacted to form the required product after passing through the catalyst. The heat of reaction is quickly transferred from the reaction site to the outer wall of the tube. The coolant circulated or boiling on the shell side removes the heat of reaction. Typically, the oxygen component of the reactants should be kept low so that the hydrocarbon-oxygen mixture is outside of the explosion limits and also to minimize the formation of carbon dioxide, which is a complete oxidative byproduct.

Commonly used tubular reactor cooling methods include a method of forced circulation of an appropriate heat transfer liquid and a method of boiling. If heat transfer is poor between the reactor tube and the heat transfer liquid, the temperature distribution along the length of the reactor tube will not be good. Typically, the temperature distribution of the exothermic catalysis is low at the free end, maximal at the center tube portion, and drops as the reactant disappears. Thus, the gaseous tubular catalysis reactor in which the bed is fixed will exhibit an unnecessary temperature "rise" or "cold spot".

If the reactor temperature exceeds the optimum temperature for a given reaction, the selectivity is low because unwanted products are formed. Unnecessary side reactions also result in local hot spots that can carbonize the organic heat transfer liquid. One reaction that can lead to this condition is the partial oxidation of ethylene, which generates significant heat in ethylene oxide; at this time, heat transfer liquids typically use DOTTHERM or tetrahydronaphthalene or similar HTF.

The temperature distribution of the catalytic tubular reactor changes with time when the catalyst is deactivated. In general, the cold spot of the catalytic tubular reactor tends to move from the inlet end to the outlet end. Several methods have been proposed for controlling cold spots in catalytic tubular reactors, but have proved undesirable because they result in side effects that are not substantial or that the selectivity is reduced. Such a conventional method is as follows.

US Patent No. 4.261.899 to Gelbine, which discloses the use of a dilute phase transfer bed (riser reactor) and fluidized bed heat exchanger of varying diameters.

Single tube reactor with complex electric heater, as proposed by M. Yoshida and S. Matsumoto (Journal of Chemical Engineering of Japan, Vol. 31, Part 3, pages 381-390, 1998).

-A. Anastasisov and V. A. As suggested by Nikoloff (Industrial Engineering Chemicals, Vol. 37, pp. 3424-3433, 1998), the use of dual reactors in series to optimize overall performance.

A reactor with a cooling coil embedded in the catalyst bed, as disclosed in German patents 3.937.030 and JA-60-7929 and EP 337.748. This method is impractical because it is desired that the tube size (20-40 mm) be very small in the heat exchanger.

According to US Pat. No. 5.262.551, methane is used instead of nitrogen as catalyst gas. Since methane has good heat capacity and conductivity, gas heat transfer is good. The catalyst temperature is reduced to 7 ° C.

According to US Pat. No. 4,624.360, a method is disclosed in which an inert catalyst support is used to preheat the incoming gas.

None of the prior art handles local cold spots that occur when gas flow is reduced due to poor distribution or excessive pressure drop of gas in a particular tube, or when the catalyst is locally located, or when local heat transfer is compromised. It does not mention how. The problem of local cold spots is particularly cumbersome when the heat transfer liquid is sensitized to carbon blocks. Therefore, there is a need for a bed-fixed gas phase catalytic reaction reactor suitable for maintaining an essentially isothermal temperature distribution along the length of the reactor regardless of the heat load in each tube and with improved heat removal capacity. In addition, the configuration, operation and maintenance of such a reactor is preferably easy. In addition, the heat of reaction is preferably recovered to generate steam. In addition, the reactor may use a vertical tube of length not exceeding 10.67 m (35 ft) to 15.24 m (50 ft) to facilitate the replacement of fresh catalyst and removal of the used catalyst.

The chemical reactor of the present invention includes a tubular reactor formed integrally with a heat transfer device, commonly referred to as a heat pipe. As disclosed in US Patent No. 2350.348 issued to Gaugler, heatpipes utilize the evaporation of heat transfer liquid from a porous medium adhered to the heat transfer surface to absorb heat. According to the present invention, a heatpipe system is provided on at least a portion of the outer side of the tubular reactor facing the reaction mixture in the reactor tube to remove the heat of reaction from the reaction mixture by evaporative cooling from the heat transfer surface of the heatpipe system. Porous media on the heat transfer surface are commonly referred to as "wicks". Evaporation of heat transfer liquids from porous media or wicks has a very good heat transfer coefficient and basically allows for a fairly high heat flux in an isothermal state. If necessary, the evaporated heat transfer liquid is condensed and then returned to the heat transfer zone of the reactor. Because of the high heat transfer coefficient associated with condensation, the heat absorption and heat dissipation elements of the heat pipe provided to the reactor have a very high heat flux ratio.

The advantages of using a heatpipe heat transfer device on a tubular reactor as described above are the conventional bare tubes for evaporative cooling of thin films from porous surfaces where convective heat transfer or evaporated heat transfer fluid can escape easily and quickly. It is derived from the transformation, which may be evaporative cooling. Convective heat transfer is defined by a number of factors; These factors include the speed of the heat transfer liquid, the temperature difference between the reaction mixture and the coolant, the viscosity of the heat transfer liquid, the surface area available for heat transfer, the components of the heat transfer device, and the state of the heat transfer surface that may be fouled. Included. Conventional submerged tube evaporative cooling uses higher heat transfer coefficients than convective cooling, but is limited by the liquid phase surrounding the submerged tube. Heatpipes replace thin film evaporation, improving shell-side heat transfer coefficients up to 10 times for submerged tube boiling. In addition, since the heat dissipation element of the heat pipe with the tubular reactor depends on the condensation of the heat transfer liquid which may occur in the condenser spaced apart from the reactor, the heat transfer liquid that can be used for cooling need not be limited to the tubular reactor surface area. Thus, a condenser having a surface area sufficient to handle the required heat flux can be located at, but close to, the tubular reactor of the present invention.

Since the evaporation of the pure heat transfer liquid of the heat pipe heat transfer system of the present invention occurs at a single temperature, and the heat transfer coefficient of the heat pipe heat transfer apparatus of the present invention is very good, the tubular reactor equipped with the heat pipe heat exchanger according to the present invention is Basically it can be operated in an isothermal state. Since the heat transfer coefficient for thin film heatpipe evaporation is considerably larger than the heat transfer coefficient of submerged tube evaporation, the reactor of the present invention has a heat flux greater than that generated in conventional cooling.

As described in Peterson (John Wesley & Sons, 1994, "Introduction to Heatpipes") and Pagri (Taylor & Francis, 1995, "Heatpipe Science and Technology", the choice of materials and the choice and heat transfer The design of the wick structure for the heat pipe apparatus of the invention will be appreciated by those skilled in the art The constituent material in contact with the heat transfer liquid is typically selected from copper, copper alloy, aluminum and its alloys, stainless steel do.

Although the term heat "pipe" is used in the present invention, many other forms may be used that differ from conventional cylindrical pipes. For example, flat, rectangular, annular, polygonal, and tubular may also be used, but are not limited thereto.

Heat pipe heat transfer system of the present invention by evaporating the liquid heat transfer liquid evaporator portion, the heat absorbing portion, the heat insulating portion through which the evaporated heat transfer medium can flow without changing the state, and the evaporated heat transfer liquid condensed by an external cooling source It consists of two or three parts, such as a condensation unit. Heat transfer condensate may be returned to the evaporator portion of the tubular reactor by gravity or pumping. In the evaporator portion of the heat pipe heat transfer system of the present invention, the heat transfer liquid is supplied to the reservoir at the bottom of the wick type heat pipe surface, and the wicking of the porous surface or wick wets the heat pipe with a thin film of heat transfer liquid. Since the wicking is a surface tension phenomenon defined by the long heat pipe by the head, it is sometimes desirable for the tubular reactor of the present invention to have a heat pipe heat transfer portion which can be divided into a plurality of heat pipe heat transfer zones, each of which has a heat transfer. The regions each have a wick height that can be wetted by capillary action of the heat transfer liquid in the wick.

In one embodiment of the present invention, a liquid heat transfer source capable of well cleaning the boiler feed water may supply an evaporator portion of the reactor heatpipe, which may be connected to a vapor header such as a steam header. Can be. In this way, the tubular reactor according to the present invention can be used to produce useful steam from reactor waste heat, eliminating the need for a reactor cooler / condenser.

The reaction temperature of the tubular reactor of the present invention is controlled by the boiling point of the heat transfer liquid. By changing the pressure of the heat transfer liquid, it is possible to change the boiling point of the heat transfer liquid.

Despite the fact that the tubular reactor with the heat pipe of the present invention adds an intermediate step to the entire heat transfer mechanism, the heat transfer flow rate of the reactor portion with the heat pipe can be increased to several orders of magnitude from the conventional submerged tube evaporative heat exchange. Can be. Excellent performance is maintained by the rapid heat transfer rate of liquid evaporation on the porous surface and the rapid transfer of steam from the evaporator section to the condenser section of the heat pipe.

In the reactor of the present invention, the heat transfer liquid is selected such that there is no malfunction of the heat pipe depending on the operating temperature. This heat transfer liquid is selected from the liquid having the boiling point required at the set operating pressure. Common heat transfer solutions are water, acetone, alkanes, ammonia, carbon fluoride, and aromatic solvents and pure liquid metals.

The wick used in the present invention may be composed of a fiber mat, a spherical or non-spherical sintered metal powder of one or more sizes, and a single or multiple layers of metal screen, all of which are fins. It may or may not have a surface hardening, such as fin.

In most cases, solid catalyst pellets are built into the tube side of the reactor through which gas reactants flow. The tube side of the reactor of the present invention is the same as all conventional tubular reactors.

The tubular reactors of the present invention equipped with heat pipes remain isothermal under appreciable significant heat flux variations. This deviation occurs when the local spot starts. As an example, partial oxidation of ethylene to ethylene oxide results in complete oxidation of ethylene on carbon dioxide due to local cold spots. This side reaction generates 12.6 times more heat than the reaction required for ethylene oxide. If the increased heat is not removed, the reactor temperature becomes excessively high, deteriorating reactor selectivity, and even worse heat transfer on the shell side, ultimately damaging the entire reactor. The reactor of the present invention with a heat pipe responds to this high temperature heat flux state through an increased evaporation rate at the same temperature. Thus, it is possible to control the malicious reaction itself.

Of course, the increased heat removal in the cold spot region of the tubular reactor is a significant advantage. Despite the intense heat generation, local cold spots that cause malignant reactions can be eliminated. Thus, the elevated temperature distribution of the exothermic catalysis becomes flat, and the reactor of the present invention is operated with optimum selectivity.

The reactor structure of the present invention is simpler than conventional tubular reactors. For example, the temperature required for an ethylene oxide reactor using direct steam generation is 200 ° C., which corresponds to a steam pressure of 220 psia. However, due to the hot spots typically encountered in conventional ethylene oxide reactors, the reactor vessel must be designed at a temperature of 250 ° C. corresponding to a steam pressure of 566 psia. Designing for high pressures requires significant costs. For this reason, water, which is preferable in terms of cost and operation as the heat transfer liquid, should be replaced by a hydrocarbon-based heat transfer liquid having a low boiling point.

Another advantage of the present invention is that when an operator error or equipment failure occurs, the coolant level can be lowered below its normal operating level in the reactor. In conventional reactors, cold spots quickly occur at the top of the reactor. If the reactor tube of the reactor of the present invention has a porous surface below the coolant normal operating level of the reactor over the entire length or at least a portion of the length, the reactor of the present invention is locked to the portion of the tube exposed by the falling coolant level. Since switching from the operation to the heat pipe mode, the flexibility is good. The porous surface has a wicking actuation portion that can wet the tube surface.

The present invention is not limited to using water as the heat transfer liquid. Other suitable liquids that can be added to the reaction temperature can also be used as heat transfer liquids. By appropriate reactor design, the temperature distribution of the tubular reactor of the present invention can be controlled to within 1 ° C over the tube length.

The constituent material in contact with the liquid inside may be copper, copper alloy, aluminum and its alloys, stainless steel and nickel alloys. If the material in contact with the internal liquid is incompatible with the treatment liquid, two different materials may be used in the form of plating, lining or coating. The internal liquid is selected such that there is no malfunction of the heat pipe depending on the operating temperature range.

Such heat transfer solutions are water, acetone, alkanes, ammonia, carbon fluoride, aromatic solvents and pure liquid metals. The structure of the wick may be composed of one or more types of spherical or non-spherical sintered metal powder and single or multiple layers of metal screens, all of which may or may not have an outer surface.

The catalytic tubular reactor according to the invention comprises a tube filled with porous catalyst pallets. The tubes containing the catalyst have a length of about 10.67 m (35 ft) to 15.24 m (50 ft). Reactor tube length is governed by practical matters such as assembly processes, and maintenance is not critical to the present invention. Bed temperature varies along tube length as a function of catalyst life. In general, the reactor cold spot associated with most of the active reactor portion moves towards the reactor outlet as the catalyst in the reactor becomes inactive over its lifetime. To deal with moving reactor cold spots, the reactor of the present invention includes a heatpipe cooling system over a tube length that corresponds to the predicted cold spot of the reactor when the catalyst in the reactor is replaced and when the catalyst is used.

Other objects, features and advantages of the present invention will be more clearly understood by the following detailed description with reference to the accompanying drawings.

1 is a longitudinal sectional view of a tubular reactor according to the invention with a direct steam generator;

2 is a longitudinal sectional view of a multi-zone tubular reactor according to the present invention.

3 is a cross-sectional view of a finned reactor tube according to the present invention.

4 is a perspective view of a finned reactor tube according to the present invention;

[Description of Symbols for Main Parts of Drawing]

10 reactor 12 inlet head

20: Tube 21: Week surface

30: shell 33: tube area

In the following, a chemical reactor with a heat pipe heat transfer device and a method of using such a device for carrying out the chemical reaction will be described. In the description of the present invention, specific forms, materials, dimensions, and the like have been set by way of example only for better understanding. However, one of ordinary skill in the art appreciates that the present invention may be practiced without these specific details. In some cases, well-known devices have been used in the form of block diagrams so as to not unnecessarily obscure the present invention.

1 shows a preferred embodiment of a reactor 10 constructed in accordance with the present invention. For simplicity, the reactor 10 is shown as a single reactor tube 20. Commercial reactor 10 includes hundreds or thousands of tubes 20. Tube 20 is filled with a porous catalyst pallet (not shown). The reactor 10 can be operated in a downstream or upstream direction. For simplicity, the upstream operation is shown in FIG. The reactants are fed to the reactor 10 through an inlet nozzle 11 which is open to the reactor inlet head 12. The reactor inlet head 12 distributes the reactants in a composite tube 20 mounted to the tubesheet 13. The product from tube 20 is conveyed to outlet nozzle 5 through reactor outlet head 14.

The liquid heat transfer liquid (HTF) is supplied to the shell 30 through the HTF supply nozzle 31 to fill the shell 30 to the level (L). The tube 20 includes a weak surface 31 at its outlet end. The level L of the liquid HTF divides the reactor 10 into a submerged tube region 33 and a heat pipe region 34.

In region 33, the HTF removes heat of reaction by boiling. The heat flux capacity of the tube 20 below the liquid level L is significantly improved by the expansion of the wick surface 21 below the liquid level L, since the porous surface creates nucleation sites that promote boiling. However, a fully submerged reactor chub 20 does not act as a heat pipe even if it has a wick surface 21 in the submerged portion. The reason is that heatpipe operation requires vapor space in the region of the wick surface 21 to enable rapid vapor transfer from the evaporator portion of the heatpipe. For maximum heat transfer capability and adaptability, the overall length of the tube 20 should be covered with a porous surface, such as the wick surface 21. As the wick surface 21 extends at least a small distance below the liquid level L, the liquid level in the shell 30 drops even below the level L due to operator error or malfunction of the plant. The advantage that the heat pipe cooling of (20) is possible is achieved. The weak surface 21 is briefly submerged in the liquid HTF below the level L, and capillary action pulls the liquid HTF to the weak surface 21. The heat of reaction causes the HTF to evaporate on the weak surface 21, thereby further wetting the weak surface 21 by capillary pumping. This automatic cooling produces a uniform temperature even where the cold spot is located. HTF evaporated from submerged tube 20 in region 33 and HTF evaporated from wick surface 21 of tube 20 in region 34 flow through vapor HTF outlet 32.

If the HTF is water or any other substrate applicable to the reactor 10, the evaporated HTF can be transferred to a steam or steam header for use in various applications. Optionally, the evaporated HTF can be condensed in a condenser (not shown), and the condensate returns from the HTF feed nozzle 31 to the reactor 10 by gravity or pumping.

The length of the heat pipe region 34 is defined by the maximum capillary height. If desired, several heatpipe regions may be provided to cover the long portion of the tubular reactor. At the bottom of each heatpipe region 34 must be provided an HTF reservoir / distributor.

Capillary action is commonly used in heat pipes. However, due to vertical long pipes exceeding several feet, the surface tension upon which capillary action depends is insufficient to overcome the hydrostatic pressure acting on the vertical long pipes. In this state, another embodiment of the present invention as shown in Fig. 2 is used. 2 shows a multi-zone tubular reactor 100 composed of separate heat transfer evaporation zones. For simplicity of illustration, reactor 100 includes one reactor tube 110 and four evaporation zones 101 to 104. Commercial reactor 100 includes hundreds or thousands of tubes 110. Tube 110 is filled with a porous catalyst pallet as shown in FIG.

Tube 110 is mounted to reactor shell 120 between tube sheets 121. The reactants are fed from the reactor inlet head 122 to the top of the reactor 100 and then distributed between the tubes 110. The reactants flow downward through the porous catalyst pallet 220 in the tube 110, but may also flow in the reverse direction. Unconsumed reactants and products and reaction byproducts flow from the bottom of the tube 110 to the reactor outlet head 123 and then to the outlet reactor 100.

The liquid HTF is led to separator 130 through conduit 133 and then distributed to heat pipe distributor 125 by HTF supply conduit 131. The distributor 125 is a complete baffle plate that is perforated to pass through the reactor tube 110. The penetration of the distributor 125 is not tightly inserted so that a portion of the liquid HTF can leak out of the heatpipe region through the wick surface 111. The vapor HTF is discharged from the top of the evaporation zones 101 to 104 through the conduit 132 and then flows into an entrainment separator 130 which acts as a preheater for the liquid heat transfer liquid supply 133. The porous wick surface 111 may be applied to the tube 110 in all evaporation zones 101 to 104 and may optionally be applied to one or more of the evaporation zones.

The liquid HTF is maintained at the level L1 on the distributor 125 in the regions 101-104 by controlling the flow of the liquid HTF by the control valve 135. Thus, the distributor 125 acts as a reservoir of liquid HTF on the wick surface 111 and below the wick surface in each vaporization region 101-104.

In tightly packed tube bundles, it is very difficult to distribute the liquid HTF evenly on the tube. The use of more than one distributor can solve this problem.

The wicked heatpipe surface on the outside of the reactor tube 110 may be composed of spherical or different shaped sintered metal powder, sintered metal fiber, or a metal mesh with or without fins. The mesh fin 211 as shown in the tube 210 in FIGS. 3 and 4 can increase the evaporation area considerably, such as a cold spot region where the heat flux may exceed the normal capability provided by the tube 110. The heat flux in each region of the reactor tube can be significantly reduced.

The reactor tubes according to the invention can have a variety of sizes, but seamless tubes of 3/4 inch or 1.5 inch diameter are preferred. Smaller diameter tubes increase the heat transfer area per unit reaction volume, but smaller tubes reduce the use of reactor volume due to poor catalyst packing and increase the potential for catalyst bridging. This problem results in uneven flow distribution. The tube thickness is set based on the processing pressure. The reactor tube according to the invention is made of a metal that can withstand chemical treatment. The thickness of the weak surface 21 and the weak heat pipe surface 111 generally does not exceed 1 mm.

The present invention has been described with reference to the preferred embodiments, and is not limited thereto, and one of ordinary skill in the art should recognize that various modifications and changes can be made to the present invention without departing from the appended claims.

Claims (14)

In a tubular reactor for carrying out a chemical reaction with exothermic heat of reaction, At least one thermally conductive reactor tube extending between the at least two tube plates in the heat exchanger shell, The reactor tube has an open feed end for directing the reactor into the reaction zone inside the reactor tube and an open outlet end for guiding the reaction product from the reactor tube; The adiabatic reactor tube comprises an outer heat transfer tube surface between the tube plates and inside the heat exchanger shell; Wherein said outer heat transfer tube surface comprises at least one heat pipe heat transfer device for inducing an exothermic reaction heat from said thermally conductive reactor in an isothermal state. The method of claim 1, wherein the reactor tube has a constant length; A portion of the reactor tube corresponds to the cold spot in the reaction zone and produces heat that exceeds the average heat generation per unit of unit reactor tube length; Said heat pipe heat transfer apparatus being located on a cold spot. The tubular reactor of Claim 1, wherein the reactor has a constant length and the heatpipe heat transfer device is located on the reactor tube over its entire length. 2. The reactor of claim 1, wherein the reactor tube has a constant length and the heat exchanger shell includes a fluid reservoir for supporting a liquid heat transfer liquid to a portion of the heat exchanger shell; The reactor tube extends through the fluid reservoir; The heat pipe heat transfer device extends through the fluid reservoir and is positioned on a reactor tube extending beyond the fluid reservoir along the length of the reactor tube so that heat transfer liquid in the fluid reservoir is transferred from the fluid reservoir by the heat pipe heat transfer device. A tubular reactor, characterized in that it is formed wicked up to an adjacent portion of the tube. 5. The heat exchanger shell of claim 4, wherein the heat exchanger shell includes a plurality of spaced fluid reservoirs to support the liquid heat transfer liquid, and wherein the thermally conductive reactor tubes extend through the plurality of fluid reservoirs to thereby heat pipe heat transfer between the fluid reservoirs. A tubular reactor characterized by forming a region. 6. The tubular reactor of Claim 5, further comprising means for transferring the liquid heat transfer liquid to the fluid reservoir. The tubular reactor of claim 1, wherein the reactor tube is positioned vertically in a heat exchanger. The tubular reactor of claim 6, wherein the reactor tube is positioned vertically in the heat exchanger. 2. The tubular of claim 1, wherein the heat exchanger shell includes a heat transfer inlet for transferring a liquid heat transfer liquid to the reactor tube and a heat transfer outlet for transferring the evaporated liquid heat transfer liquid from the heat exchanger. Reactor. 7. The tubular of claim 6, wherein the heat exchanger shell comprises a heat transfer inlet for transferring a liquid heat transfer liquid to the reactor tube and a heat transfer outlet for transferring the evaporated liquid heat transfer liquid from the heat exchanger. Reactor. The tubular reactor of Claim 1, wherein the heatpipe heat transfer device comprises a porous heat transfer surface on the reactor tube. The tubular reactor of claim 6, wherein the heatpipe heat transfer device comprises a porous heat transfer surface on the reactor tube. 12. The tubular reactor of claim 11, wherein the porous heat transfer surface is increased by porous fins. 13. The tubular reactor of claim 12, wherein the porous heat transfer surface is increased by porous fins.